The following abbreviations are herewith defined, at least some of which are referred to within the following description about the prior art and the present invention.
3GPP 3rd Generation Partnership Project
AECID Adaptive E-CID
A-GNSS Assisted-GNSS
A-GPS Assisted-GPS
ANR Automatic Neighbor Relation
AoA Angle-of-Arrival
BS Base Station
CDMA Code Division Multiple Access
CQI Channel Quality Indicator
CRS Cell Specific Reference Signals
DRX Discontinuous Reception
E-CID Enhanced Cell Identification
eICIC Enhanced Inter-cell Interference Coordination
eNodeB Evolved Node B
E-SMLC Evolved SMLC
E-UTRAN Evolved UTRAN
GMLC Gateway Mobile Location Centre
GNSS Global Navigational Satellite System
GPS Global Positioning System
GSM Global System for Mobile Communications
LBS Location-Based Service
LCS Location Services
LPP LTE Positioning Protocol
LPPa LPP Annex
LTE Long-Term Evolution
MDT Minimization of Drive Tests
MME Mobile Management Entity
MST Multi-Standard Radio
O & M Operations & Maintenance
OMA Open Mobile Alliance
OTDOA Observed Time Difference of Arrival
PCI Physical Cell Identity
PDN GW Packet Data Network Gateway
P-GW Packet-Gateway
PRS Positioning Reference Signal
RAN Radio Access Network
RAT Radio Access Technology
RB Resource Block
RRC Radio Resource Control
RRM Radio Resource Management
RS Reference Signal
RSRP Reference Signal Received Power
RSRQ Reference Signal Received Quality
RSSI Received Signal Strength Indicator
RSTD Reference Signal Time Difference
S-GW Serving-Gateway
SLP SUPL Location Platform
SLC SUPL Location Center
SMLC Serving Mobile Location Center
SON Self Organizing Network
SPC Signalling Point Code
SUPL Secure User Plane Location
TA Timing Advance
UE User Equipment
UMTS Universal Mobile Telecommunications System
UTDOA Uplink Time Difference Of Arrival
UTRA Universal Terrestrial Radio Access
WCDMA Wideband Code Division Multiple Access
The possibility of identifying the geographical location of a user (e.g., wireless terminal, UE) in a telecommunications network has enabled a large variety of commercial and non-commercial services, e.g., navigation assistance, social networking, location-aware advertising, emergency calls, etc. Different services may have different positioning accuracy requirements which are imposed by the application. In addition, some regulatory requirements on the positioning accuracy for basic emergency services exist in some countries, i.e. FCC E911 in US.
In many environments, the position of the wireless terminal can be accurately estimated by using positioning methods based on GPS (Global Positioning System). Nowadays, telecommunication networks often have a possibility to assist UEs in order to improve the terminal receiver sensitivity and GPS start-up performance (Assisted-GPS positioning, or A-GPS). GPS or A-GPS receivers, however, may not necessarily be available in all wireless terminals. Furthermore, GPS is known to often fail in indoor environments and urban canyons. Thus, a complementary terrestrial positioning method, called Observed Time Difference of Arrival (OTDOA), has been standardized by 3GPP. In addition to OTDOA, the LTE standard also specifies methods, procedures and signaling support for Enhanced Cell ID (E-CID) and A-GNSS. Plus, a positioning method known as Uplink Time Difference Of Arrival (UTDOA) is also being standardized for LTE.
1. Positioning in LTE
The three key network elements in an LTE positioning architecture are the LCS Client, the LCS target device (e.g., terminal) and the LCS Server. The LCS Server is a physical or logical entity that manages positioning for the LCS target device by collecting measurements and other location information, assisting the terminal in measurements when necessary, and estimating the LCS target location. The LCS Client is a software and/or hardware entity that interacts with the LCS Server for the purpose of obtaining location information for one or more LCS target devices, i.e. the entities being positioned. The LCS Client may reside in the LCS target device itself. The LCS Client sends a request to the LCS Server to obtain location information, and the LCS Server processes and serves the received request and sends the positioning result and optionally a velocity estimate to the LCS Client. A positioning request can be originated from the terminal or the network.
The position calculation can be conducted, for example, by the LTE's LCS server (e.g., E-SMLC or SLP) or by the UE. The former approach corresponds to what is known as the UE-assisted positioning mode, while the latter approach corresponds to what is known as the UE-based positioning mode.
The LTE currently supports two positioning protocols namely LPP and LPPa which operate via the radio network. The LPP is a point-to-point protocol between the LCS Server and the LCS target device, used in order to position the target device. LPP can be used both in the user and control plane, and multiple LPP procedures are allowed in series and/or in parallel thereby reducing latency. LPPa is a protocol between the eNodeB and the LCS Server and is specified only for control-plane positioning procedures, although it still can assist user-plane positioning by querying eNodeBs for information and eNodeB measurements. In this case, the SUPL protocol can be used as a transport for LPP in the user plane. The LPP also has a possibility to convey LPP extension messages inside LPP messages, e.g., currently OMA LPP extensions are being specified (LPPe) to allow, e.g., for operator- or manufacturer-specific assistance data or assistance data that cannot be provided with LPP or to support other position reporting formats or new positioning methods. The LPPe may also be embedded into messages of other positioning protocol, which is not necessarily LPP.
A high-level architecture of a radio network 100, as it is currently standardized in LTE, is illustrated in FIG. 1 (PRIOR ART), where the LCS target is a terminal 102, and the LCS Server is an E-SMLC 104 or an SLP 106. In this figure, the control plane positioning protocols with the E-SMLC 104 as the terminating point are LPP, LPPa and LCS-AP, and the user plane positioning protocol is SUPL and SUPL/LPP. The SLP 106 may comprise two components SPC 108 and SLC 110 which may also reside in different nodes. In an example implementation, the SPC 108 has a proprietary interface with the E-SMLC 104, and an LLP interface with the SLC 110 while the SLC 110 communicates with a P-GW 112 (PDN-Gateway 112) and an external LCS Client 114. One skilled in the art will recognize and understand this high-level architecture of the radio network 100 including the eNodeB 116, the GMLC 118, the MME 120, the S-GW 122, the RAN 126, and the core network 128. Additional positioning architecture elements may also be deployed to further enhance performance of specific positioning methods. For example, deploying radio beacons 130 (two shown) is a cost-efficient solution which may significantly improve positioning performance indoors and also outdoors by allowing more accurate positioning, for example, with proximity location techniques.
2. Positioning Methods
To meet LBS demands, the LTE network deploys a range of complementing positioning methods characterized by having different performances in different environments. Depending on where the measurements are conducted and the final position is calculated, the positioning methods can be UE-based, UE-assisted or network-based, each with their own advantages. The following positioning methods are available in the LTE standard for both the control plane and the user plane:                Cell ID (CID),        UE-assisted and network-based E-CID, including network-based angle of arrival (AoA),        UE-based and UE-assisted A-GNSS (including A-GPS),        UE-assisted Observed Time Difference of Arrival (OTDOA).        
Hybrid positioning, fingerprinting positioning/pattern matching and adaptive E-CID (AECID) do not require additional standardization and are therefore also possible to be implemented in the LTE network. Furthermore, there may also be UE-based versions of the positioning methods above, e.g. UE-based GNSS (e.g. GPS) or UE-based OTDOA, etc. There may also be some alternative positioning methods such as proximity based location. UTDOA may also be standardized in a later LTE release, since it is currently under discussion in 3GPP. More methods, LTE and non-LTE, are supported with LPPe. Similar positioning methods, which may have different names, also exist in other RATs, e.g., CDMA, WCDMA or GSM.
2.1 E-CID Positioning
The E-CID positioning method exploits the advantage of low-complexity and fast positioning with CID which exploits the network knowledge of geographical areas associated with cell IDs, but enhances positioning further with more measurement types. With Enhanced Cell ID (E-CID), the following sources of position information are involved: the Cell Identification (CID) and the corresponding geographical description of the serving cell, the Timing Advance (TA) of the serving cell, and the CIDs and the corresponding signal measurements of the cells (up to 32 cells in LTE, including the serving cell), as well as AoA measurements. The following UE measurements can be utilized for E-CID in LTE: (1) E-UTRAN carrier Received Signal Strength Indicator (RSSI); (2) Reference Signal Received Power (RSRP); (3) Reference Signal Received Quality (RSRQ); and (4) UE Rx-Tx time difference. The E-UTRAN measurements available for E-CID are eNodeB Rx-Tx time difference (also called TA Type 2), TA Type 1 being (eNodeB Rx-Tx time difference)+(UE Rx-Tx time difference), and UL AoA. The UE Rx-Tx measurements are typically used for the serving cell, while e.g. RSRP and RSRQ as well AoA can be utilized for any cell and can also be conducted on a frequency different from that of the serving cell. The UE E-CID measurements are reported by the UE 102 to the positioning server (e.g. Evolved SMLC, or E-SMLC 104, or SUPL Location Platform, or SLP 106, in LTE) over the LTE Positioning Protocol (LPP), and the E-UTRAN E-CID measurements are reported by the eNodeB 116 to the positioning server 104 over the LPP Annex protocol (LPPa). The UE 102 may receive assistance data from the network e.g. via LPPe (no LPP assistance for E-CID is currently specified in the standard, however, it may be sent via LPP extension protocol, LPPe).
2.2 OTDOA Positioning
The OTDOA positioning method makes use of the measured timing of downlink signals received from multiple eNodeBs 116 (one shown in FIG. 1) at the UE 102. The UE 102 measures the timing of the received signals using assistance data received from the LCS server 104 and 106, and the resulting measurements are used to locate the UE 102 in relation to the neighbouring eNodeBs 116.
In the OTDOA positioning method, the terminal 102 (UE 102) measures the timing differences for downlink reference signals received from multiple distinct locations. For each (measured) neighbor cell, the UE 102 measures Reference Signal Time Difference (RSTD) which is the relative timing difference between neighbor cell and the reference cell. The UE position estimate is then found as the intersection of hyperbolas corresponding to the measured RSTDs. At least three measurements from geographically dispersed base stations (eNodeBs 116) with a good geometry are needed to solve for two coordinates of the terminal 102 and the receiver clock bias. In order to solve for position, precise knowledge of the transmitter locations and transmit timing offset is needed.
To enable positioning in LTE and facilitate positioning measurements of a proper quality and for a sufficient number of distinct locations, new physical signals dedicated for positioning (positioning reference signals, or PRS) have been introduced and low-interference positioning subframes have been specified in 3GPP.
The PRS are transmitted from one antenna port (R6) according to a pre-defined pattern. A frequency shift, which is a function of Physical Cell Identity (PCI), can be applied to the specified PRS patterns to generate orthogonal patterns and modeling the effective frequency reuse of six, which makes it possible to significantly reduce neighbour cell interference on the measured PRS and thus improve positioning measurements. Even though PRS have been specifically designed for positioning measurements and in general are characterized by better signal quality than other reference signals, the standard does not mandate using PRS. Other reference signals, e.g. cell-specific reference signals (CRS) may also be used for positioning measurements.
The PRS are transmitted in pre-defined positioning subframes grouped by several consecutive subframes (NPRS), i.e. one positioning occasion. Positioning occasions occur periodically with a certain periodicity of N subframes, i.e. the time interval between two positioning occasions. The standardized periods N are 160, 320, 640, and 1280 ms, and the number of consecutive subframes may be 1, 2, 4, or 6.
3. Inter-Frequency, Inter-Band and Inter-Rat Measurements
It is mandatory for all UEs to support all intra-RAT measurements (i.e. inter-frequency and intra-band measurements) and meet the associated requirements. However the inter-band and inter-RAT measurements are UE capabilities, which are reported to the network during the call setup. The UE supporting certain inter-RAT measurements should meet the corresponding requirements. For example a UE supporting LTE and WCDMA should support intra-LTE measurements, intra-WCDMA measurements and inter-RAT measurements (i.e. measuring WCDMA when serving cell is LTE and measuring LTE when serving cell is WCDMA). Hence, the network can use these capabilities according to its strategy. These capabilities are highly driven by factors such as market demand, cost, typical network deployment scenarios, frequency allocation, etc. The UE 102 may also report specifically for the positioning purpose, e.g. upon a network request, the set of supported frequency bands.
3.1 Inter-Frequency Measurements
Inter-frequency measurements may in principle be considered for any positioning method, even though currently not all measurements are specified by the standard as intra- and inter-frequency measurements. The examples of inter-frequency measurements currently specified by the standard are Reference Signal Time Difference (RSTD) used for OTDOA, RSRP and RSRQ which may be used e.g. for fingerprinting or E-CID. There are, however, no requirements for inter-frequency E-CID measurements.
The UE performs inter-frequency and inter-RAT measurements in measurement gaps. The measurements may be done for various purposes: mobility, positioning, self organizing network (SON), minimization of drive tests etc. Furthermore the same gap pattern is used for all types of inter-frequency and inter-RAT measurements. Therefore, E-UTRAN must provide a single measurement gap pattern with constant gap duration for concurrent monitoring (i.e. cell detection and measurements) of all frequency layers and RATs.
In LTE, the measurement gaps are configured by the network to enable measurements on the other LTE frequencies and/or other RATs (e.g. UTRA, GSM, CDMA2000, etc). The gap configuration is signaled to the UE over RRC protocol as part of the measurement configuration. If the UE requires measurement gaps for OTDOA positioning measurements then it may send an indication to the network, e.g. eNodeB, upon which the network may configure the measurement gaps. Furthermore, the measurement gaps may need to be configured according to a certain rule, e.g. inter-frequency RSTD measurements for OTDOA require that the measurement gaps are configured according to the inter-frequency requirements in 3GPP 36.133, Section 8.1.2.6, release 9 version 9.4.0 (2010-06), e.g. gap pattern #0 shall be used when inter-frequency RSTD measurements are configured and there should not be measurement gaps overlapping with PRS occasions of cells in the serving frequency.
3.2 Inter-RAT Measurements
In general, in LTE the inter-RAT measurements are typically defined similar to inter-frequency measurements, e.g. they may also require configuring measurement gaps like for inter-frequency measurements, but just with more measurements restrictions and often more relaxed requirements for inter-RAT measurements. As a special example, there may also be multiple networks using the overlapping sets of RATs. The examples of inter-RAT measurements specified currently for LTE are UTRA FDD Common Pilot Channel (CPICH) Received Signal Code Power (RSCP), UTRA FDD carrier RSSI, UTRA FDD CPICH Ec/No, GSM carrier RSSI, and CDMA2000 1xRTT Pilot Strength.
For positioning, assuming that LTE FDD and LTE TDD are treated as different RATs, the current standard defines inter-RAT requirements only for FDD-TDD and TDD-FDD measurements, and the requirements are different in the two cases. There are no other inter-RAT measurements specified within any separate RAT for the purpose of positioning and which are possible to report to the positioning node (e.g. E-SMLC in LTE).
Inter-RAT positioning measurement reporting may be possible with LPPe. However, for UEs requiring measurement gaps the current standard does not allow configuring the gaps for other than inter-frequency RSTD measurements.
3.3 Inter-Band Measurements
An inter-band measurement refers to the measurement done by the UE on a target cell on the carrier frequency belonging to the frequency band which is different than that of the serving cell. Both inter-frequency and inter-RAT measurements can be intra-band or inter-band.
The motivation of inter-band measurements is that most of the UEs today support multiple bands even for the same technology. This is driven by the interest from service providers; a single service provider may own carriers in different bands and would like to make efficient use of carriers by performing load balancing on different carriers. A well known example is that of multi-band GSM terminal with 800/900/1800/1900 bands.
Furthermore, the UE may also support multiple technologies e.g. GSM, UTRA FDD and E-UTRAN FDD. Since all UTRA and E-UTRA bands are common, the multi-RAT UE may support same bands for all the supported RATs.
4. Positioning Measurement Requirements in LTE
For E-CID, there are intra-frequency UE Rx-Tx accuracy and reporting delay requirements. No inter-frequency requirements are currently defined for E-CID measurements.
OTDOA uses RSTD measurements performed by the UE. For UE-assisted OTDOA, i.e., when the UE reports the measurements to the positioning node (e.g., E-SMLC), the following requirements have been defined:                Intra-frequency RSTD accuracy requirements,        Inter-frequency RSTD accuracy requirements,        Intra-frequency RSTD reporting delay requirements for FDD,        Intra-frequency RSTD reporting delay requirements for TDD,        Inter-frequency RSTD reporting delay requirements for FDD-FDD,        Inter-frequency RSTD reporting delay requirements for TDD-FDD,        Inter-frequency RSTD reporting delay requirements for TDD-TDD,        Inter-frequency RSTD reporting delay requirements for FDD-TDD.For each of the inter-frequency requirements, two scenarios are considered:        Scenario 1: inter-frequency RSTD measurements are performed over the reference cell and neighbour cells, which belong to the inter-frequency carrier frequency f2.        Scenario 2: inter-frequency RSTD measurements are performed over the reference cell and the neighbour cells, which belong to the serving carrier frequency f1 and the inter-frequency carrier frequency f2, respectively.        
Scenario 1 corresponds to Note 1 in, e.g., Table 8.1.2.6.1-1 of the aforementioned 3GPP 36.133 standard, while Scenario 2 corresponds to Note 2 in the same table.
The requirements are generic with respect to the frequency channels and frequency bands, to i.e. the requirements are the same for any two different f1 and f2, independently on their absolute and relative location in the spectrum, e.g., being common for inter-frequency intra-band and inter-band. This generic approach with regard to the frequency channels and bands has been used for the specification of the other measurement requirements e.g. mobility measurement requirements such as RSRP and RSRQ in LTE. Note also that the requirements are currently common for inter-frequency. Furthermore, there may also be inter-RAT measurements, e.g., a UE connected to CDMA is performing LTE RSTD measurements.
To ensure that the positioning requirements are met, test cases have been specified by the standard, based on which the UEs are tested. The currently specified positioning test cases assume that the timing information for at least one cell (serving cell) in the assistance data is known to the UE, i.e., the UEs in the tests are not required to acquire the timing information of any of the cells. In these tests, the UE is required to report the positioning measurements (i.e. RSTD) within the test requirements. Failure to do so shall lead to the failure of the test. Hence, if prior to the start of the actual test the UE under test does not have the timing information of any of the cells to be measured for positioning, then it is quite likely that the UE will fail the test.